The study emphasizes how the innumerable gut bacteria affect behavior – in mice.

You’ve got 100 trillion inside your gut, by the way.

The Study

Two groups of rodents get a diet differing in containing lactobacillus rhamnosus. Lacto of course means milk – you find this bacterium hanging around your average cup of yogurt.

As in many rodent studies, the poor fellows are stressed and stressed again – made to run through mazes, or in the experiment beloved of pharmaceutical companies, forced to swim without rest and without escape – the “learned helplessness” model used to test antidepressants. And unlike in human studies, the animals are periodically surgerized and sacrificed to see what’s happening inside gut and brain.

The Results

1. The lactobacillus fed mice have different amounts of GABA, the brain’s main inhibitory transmitter, especially in places involving planning and emotion.

2.The lactobacillus mice have lower stress hormones.

3. Put in a learned helplessness model, the lactobacillus fed mice keep swimming a lot longer, not giving up. They also show more novelty seeking behavior.

4. Cut the vagus nerve – the longest nerve in our body that famously connects the brain with the heart and the gut – and all the changes disappear.

Of Mice and Men

No, mice are not the same as people. We do share a lot of physiology and mental function, but as Judah Folkman famously said, “We can curve most tumors – in the mouse.”

The human body seems to be a far more complex information system than the mouse, though we have similar amounts of different genes.

However, viruses like adenovirus have been implicated in making humans fat. There is far more serotonin in your gut than in your brain – and the gut’s many neural connections often make it called the “second brain.” Some studies hint at changing bacteria as changing the mental mood of irritable bowel syndrome sufferers.

And the effects in this study of changing gut bacteria were truly widespread. Getting animals to swim longer in a learned helplessness test is usually, though not always, obtained by giving them antidepressants.

What if you got the same affect with lactobacilli?

Implications

Three major take homes from studies like this one are:

1. You are an ecosystem. Remember all those adds for household agents to “rid yourself of harmful bacteria?” Well you’ve got a lot of bacteria. You need them for your survival.

There are approximately 27,000 human genes producing a protein or more. There are about 3,000,000 individual and different bacterial genes secreting proteins in your gut.

We’re outgunned a 100 to 1 in our GI tract – and that is not to mention all the fungi, ricketsia, protozoans, and viruses hanging around in every other nook and cranny you’ve got. No wonder about 8% of human DNA comes from retroviruses, of which the best known is AIDS. And it’s perhaps no wonder your gut lining reproduces itself in about a day – trying to deal and control the unruly 100 trillion critters with which it must contend.

2. Your body works as an information system. It may be a stretch to think of your body’s bacteria as controlling your moods. But it is in some ways a bigger stretch to note in this study that mood and stress changes shifted by simply cutting the vagus nerve – as if that single information channel was channeling gut information to the brain.

Everything is connected to everything else – funneling information back and forth as long as you are alive.

3. Information informs regeneration. Your brain and body change all the time – including the time it took to read this sentence. We regrow, renew, replace and remake ourselves depending on information flow.

In this present study, animals’ stress level, mood, adaptability and interest changed by adding one type of bacteria to their gut. Undoubtedly that changed the dynamics of all the other trillions of bacteria living there.